So I'm trying to study thermodynamics and I came across enthalpy, defined as the internal energy plus the product of pressure and temperature and the change in enthalpy being the change in those three variables. My question is, why not just use those three variables? Why is their another term for this? It just seems really abstract and unnecessary to me. Can anyone explain?
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Enthalpy is energy plus PV, not PT.
The way I've seen it described conceptually (from Schroeder Thermal Physics) is this:
Enthalpy is the total energy you need to create on object out of nothing and place it in some environment. In order to create an object you definitely need the (internal) energy of that object, but that isn't all you need. You also need energy to do work to move all of the air (or whatever else is in the way) at the location where you are creating the object, which is PV.
For more info see page 33 of Schroeder Thermal Physics.
roshoka
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